This application claims the priority of 198 21 952.0, filed May 15, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an energy supply unit for use on board an aircraft, particularly a passenger plane.
Normally, the following energy sources exist on board a passenger plane:
Main Power Unit Generator
The main power units of an airplane are used primarily to generate a thrust to propel the airplane. In addition, however, they also supply compressed air for the air conditioner and power for a power generator which energizes the electrical system of the airplane. The main power units are supplied with fuel by the fuel system of the airplane.
Auxiliary Power Unit (APU)
In airplanes, a gas turbine--the auxiliary power unit (APU)--situated in the rear of the airplane supplies the airplane current and compressed air for the air conditioner and for starting the engines. It is used on the ground as well as during the flight (for example, when starting/landing or in emergency situations). The APU is supplied with fuel by the fuel system of the airplane. In addition to generating compressed air for the air conditioner and the power unit start per integrated compressor, the APU drives a generator for generating power.
Ram Air Turbine (RAT)
An air turbine situated in the fuselage of an airplane can be moved out into the flow around the fuselage. In an emergency (such as failure of the airplane hydraulic system), by means of a coupled hydraulic pump it supplies a hydraulic system of the airplane which is sufficiently dimensioned for emergency landings. On average, this RAT is used 1 to 3 times per useful life of the airplane (25 years). Because of the dependence on the aerodynamic flow around the fuselage, its reliability is currently somewhat problematic.
NiCd-Battery
A NiCd battery packet is used to supply power to the airplane electrical system. At the time of the start of the airplane operation, this packet is used for the first self-sufficient electric energy supply on board.
Compressed Air for Driving a Compressor/Expander Unit for the Air Conditioning within the On-Board Air Conditioning System
The air-conditioning system in an air plane is switched on during all flight and ground standing times. This air-conditioning system is supplied with hot compressed air from the main power units or from the auxiliary power unit (APU). Air conditioning is performed by cooling with external air, a compressor/expander unit and a water extraction unit. The energy source for the operation of the compressor/expander unit is the compressed air coming from the main power unit or the auxiliary power unit.
German Patent Document DE 40 01 684 A1 discloses a hybrid system for driving a vehicle which comprises, in addition to an accumulator, a fuel cell as an energy supply unit.
German Patent Document DE 38 32 471 A1 discloses a fuel cell system with a freely movable electrolyte which is designed for use in zero gravity, such as in space travel.
The use of fuel cells in aviation is disclosed in German Patent Documents DE 196 00 936 A1 as well as DE 40 09 772 A1. In both cases, the electric energy generated by the fuel cell is used to drive the aircraft. However, these documents do not disclose information concerning the construction of the fuel cell system or the manner of its integration into the aircraft.
It is an object of the invention to provide an energy supply unit for use in an airplane which, in comparison to the conventional systems mentioned in the introduction to the specification, has an improved efficiency while the pollution and noise emissions are reduced.
This and other objects and advantages are achieved by the energy supply unit according to the invention, which comprises a fuel cell, particularly a Proton Exchange Membrane (PEM) fuel cell, as a power converter for generating direct current. A hydrocarbon can be used as fuel for the fuel cell and is converted to hydrogen in a reformer. However, it is also possible to carry along hydrogen in a container in the aircraft and to feed it directly to the fuel cell. The latter arrangement is particularly suitable for a hydrogen plane (currently being designed), in which hydrogen is stored in the aircraft anyhow.
Particularly in comparison to gas generators as energy converters, the advantages of the invention are as follows:
low to nil pollutant emissions PA1 lower generated noise PA1 higher efficiency PA1 lower system costs PA1 lower wear and therefore lower maintenance expenditures. PA1 1. the fuel is converted directly to current, and PA1 2. the efficiency of gas turbines is relatively poor. PA1 1. the efficiency of gas turbines is relatively poor and the FCE efficiency is very good; PA1 2. the energy conversion chain is now much simpler.
The invention is suitable for all types of aircraft; however, it is particularly suited for passenger planes and large-capacity passenger planes.
Advantageous further developments of the energy supply unit according to the invention on board an aircraft are particularly the following.
Main Power Unit Generator
The previously used gas powered generator (energy conversion: current from fuel) is replaced by a PEM fuel cell. Both a hydrocarbon (to be converted to hydrogen by a reformer in the gas generating system) and hydrogen can be used as fuels. The required air is taken from the power unit or from the outgoing cabin air. The direct current produced in the fuel cell is converted by means of an inverter into alternating current with the voltage (110V) normally used in the airplane, and is made available to the on-board power system.
By replacing the gas generators with fuel cells, the on-board current is generated with a significantly higher efficiency because
This results in a lower fuel consumption and thus in a possible saving of weight when the fuel is carried along as well as in lower emissions.
Auxiliary Power Unit (APU)
The previously used gas generator (energy conversion: compressed air and current from fuel) is replaced by a PEM fuel cell. Both a hydrocarbon (converted to hydrogen by a reformer in the gas generating system) and hydrogen can be used as fuels. A portion of the direct current produced in the fuel cell is changed by means of an inverter into alternating current, with a voltage (110 V) normally used in the airplane, and is made available to the on-board power system. Another portion is made available either as direct current or, by means of an inverter, as alternating current, to an electric motor which, in turn, drives a compressor. The required air is taken from the outgoing air (approximately 0.7 bar) of the cabin. The compressor supplies the air required for the air-conditioning system and the power unit.
The advantages achieved by replacing the gas generator in the APU by fuel cells, are the same as for the main power, as described above
Ram Air Turbine (RAT)
This energy converter (energy conversion: aerodynamic power from flow around the outside) is replaced by a PEM fuel cell drive. Both a hydrocarbon (converted to hydrogen by a reformer in the gas generating system) and hydrogen can be used as fuels. The required air is taken from the outgoing cabin air. The direct current produced in the fuel cell is converted by means of an inverter into alternating current with the voltage (110V) normally used in an airplane, and will then drive a hydraulic pump and/or supply the on-board power system.
By replacing the RAT by fuel cells, hydraulic energy or on-board current is generated in an operationally reliable manner. In addition, this system may also contribute to covering possibly occurring demand peaks in the on-board energy supply and thus represent another independent system for generating on-board current.
NiCd Battery
This energy converter (electric current from chemically stored energy) is replaced by a PEM fuel cell. Both a hydrocarbon (converted to hydrogen by a reformer in the gas generating system) and hydrogen can be used as fuels. The direct current produced in the fuel cell is changed by means of an inverter into alternating current, with the voltage (110V) normally used in the airplane, and is made available to the on-board power system. By replacing the batteries by fuel cells, the on-board current is generated with a significantly higher efficiency and it is no longer necessary to recharge the batteries so that the availability of this energy generator is increased.
Drive of a Compressor/Expander Unit for the Air-Conditioning within the On-Board Air-Conditioning System
The driving energy required for the air-conditioning system (compressed air which was generated by the gas turbine and drives a Komprex) is generated according to the invention by means of a PEM fuel cell. Both a hydrocarbon (converted to hydrogen by a reformer in the gas generating system) and hydrogen can be used as fuels. The generated electric power is made available to an electric motor either as direct current or, by way of an inverter, as alternating current. The electric motor, in turn, drives a compressor used in the air-conditioning system. The air required to operate the fuel cell is taken from the outgoing cabin air (approximately 0.7 bar). The required fresh air can be taken from the outside air by means of the compressor, for example, by way of a separate pipe and an inlet in the airplane shell. The compressor will then supply compressed air for the air-conditioning system. In emergencies, a portion of the direct current produced in the fuel cell can be converted by means of an inverter into an alternating current with the voltage (110V) normally used in an airplane, and is made available to the on-board power system.
By supplying power to the air-conditioning system by means of fuel cells, power is generated at the site with a significantly higher efficiency than by means of an APU or a main power unit because
This leads to a lower fuel consumption and thus to a possible saving of weight when fuel is carried along as well as to lower emissions.
Emergency Locator Transmitter ELT
For finding an aircraft after an emergency, airplanes contain a battery-operated ELT. In order to prolong the operating time (radio transmission time) of this system, a fuel cell system can be used, including a fueling system and an air supply system.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.